The present invention relates generally to driver or level shifter circuits, and, more particularly, to high speed circuits used, for example, to drive charge coupled devices.
High speed driver circuits, which provide level shifting between, for example, transistor-transistor logic (TTL) logic levels and high voltage levels are necessary to drive charge coupled devices (CCD), which are, for example, used in infrared focal planes. Such circuits must have high speed capability, a high output voltage swing and yet be simple enough, with minimal components, so that several such circuits may be included in a small package. The output voltage must also have very fast rise and fall times. It is also desirable that the rise and fall times be essentially the same. The fast rise and fall times are convenient for providing a high speed clock. In addition, the fast rise and fall times are necessary for the high speed operation in the CCD application. However, there are other applications where the fast rise and fall times are necessary by themselves. In fact, one application may require a very low duty cycle at relatively low frequencies, requiring, however, fast rise and fall times just so that it can go to, for example, twenty volts and back again within the available time.
It is accordingly a primary object of the present invention to provide an improved high speed driver circuit for providing an output voltage having fast rise and fall times.